The present invention relates to improved contact lens solutions that are commonly employed with plastic contact lenses.
One purpose of such solutions is to provide an aqueous solution which will wet the relatively hydrophobic plastic surface, thereby conditioning it for easier and more comfortable insertion into the eye and more comfortable wear; i.e., a cushioning effect. The wetted surface is also more readily wetted by the tears in the eye thus reducing the occurrence of dry spots. Dry spots on the surface of a contact lens cause discomfort and visual interference.
Another purpose of a contact lens solution is to provide a soaking medium which contains an antibacterial agent or an antifungicide or both. The contact lens is left to soak in this medium when not in use, as for example, overnight.
Still another purpose of a contact lens solution is to provide a cleaning action to the surface of the contact lens. Contact lenses must be handled carefully to prevent scratches and deformation, yet they must be clean to retain good visual acuity. The cleaning action must, therefore, be provided under gentle conditions of handling.
Contact lens solutions have been developed which incorporate one or more of the foregoing characteristics of wetting, soaking, cushioning and cleaning, but these compositions of the prior art have deficiencies.
For example, benzalkonium chloride, a common broad-spectrum bacteriocide which gives the positively charged benzalkonium ion in aqueous media, cannot be incorporated in solutions that contain certain negatively-charged species, e.g., anionic surfactants, because the bacteriocide is precipitated out or otherwise inactivated as an antibacterial agent when the two materials are present in the same solution. This limits the use of what is otherwise a safe and effective antibacterial agent. Another deficiency in contact lens solutions is the lack of adequate cleaning action. Anionic surfactants which are efficient cleaners cannot be used in contact lens solutions containing positively-charged antibacterial agents because of the above-noted incompatibility. Another deficiency of the usual anionic or cationic surfactants is their tendency to irritate the eye. Additionally, such cationic surfactants tend to be hydrophobic and do not give the wetting necessary or desired.